First responders (e.g., firefighters, paramedics, police officers, etc.) often need to find a person within a particular environment (e.g., within a building). In emergency situations, complete and precise information regarding a person's location are important. However, such information is often unavailable due to the technical challenges of determining a person's location within a complex environment, particularly when there is a limited amount of information about the environment or the information that is available is out of date.